The present invention relates to a fuel injection nozzle for use with a fuel injection pump for internal combustion engines, particularly for diesel engines.
In recent years, internal combustion engines have a tendency to be reduced in size, to increase in compression ratio and to increase in rotational speed. It is effective for the reduction in size to reduce the diameter of a fuel injection nozzle which is inserted into the cylinder head of the engine. In order to increase the compression ratio and to increase the rotational speed, it is strongly required to reduce the diameter of the fuel injection nozzle, particularly in the case where the nozzle is employed in an internal combustion engine of four valve type, because the nozzle-mounting space is small at the cylinder head.
Proposals have been made to meet the above requirement, as disclosed, for example, by Japanese Utility Model Publication (Kokoku) No. 53-33042, in which a fuel injection nozzle comprises a body formed with nozzle holes and a fuel inlet port for connection to a fuel injection pump, and a valve needle slidably fitted within the body for opening and closing the nozzle holes in response to the pressure of fuel delivered from the fuel injection pump into the interior of the body. The fuel inlet port communicates with the nozzle holes through a gap between the inner peripheral surface of the body and the outer peripheral surface of the valve needle. However, the conventional fuel injection nozzle is high in injection rate and short in injection period, because the valve needle is rapidly moved to open the nozzle holes at the time the pressure of fuel reaches a valve opening pressure. For this reason, in particular, when the fuel injection nozzle is applied to a diesel engine of direct-injection type, the combustion period is short, resulting in increased combustion noise. Further, irregular injection tends to occur, resulting in variation of combustion and in hunting in the engine rotation. Moreover, if a drain passage for discharging overflow fuel is provided in a wall of the body, the body is required to have its wall thickness increased. This increases the overall diameter of the fuel injection nozzle correspondingly. Thus, the provision of the drain passage in the wall of the body is an obstacle to the attempt to reduce the diameter of the fuel injection nozzle.